Mandelate racemase catalyzes the interconversion of the two enantiomers of mendelic acid. Understanding the mechanism of this enzyme may further the understanding of other enzymes that mediate proton abstraction from carbon. We are synthesizing the enantiomers of potassium a-phenylglycidate as an affinity label for Mandelate racemase. We are also synthesizing the methyl esters of the a-phenylglycidate and the corresponding diol. Further, we plan to find out which residues of Mandelate racemase are modified by a-phenylglycidate. Mass spectrometry will be used to identify the synthesized compounds and pinpoint the site(s) of modification by a-phenylglycidate. Other enzymes along the mandelate metabolic pathway may in the future be studied in similar fashion. Mass spectrometry will play a key role for future structure/function studies.